1. Field of the Invention
This invention relates to a control apparatus for a hydraulically operated vehicular transmission which is mounted on automobiles and other vehicles.
2. Description of the Related Art
A hydraulically operated vehicular transmission has a plurality of hydraulic pressure coupling elements. Those hydraulic pressure coupling elements are connected to hydraulic oil supplying paths which are connected through a shift valve to a hydraulic pressure source, so that by supplying hydraulic oil to the hydraulic pressure coupling elements, a desired gear change stage is selectively obtained.
In a control apparatus for a transmission of this type, recently, there is generally used an electronic control type control apparatus. This control apparatus is provided with electromagnetic proportional valves which control the hydraulic pressures in the hydraulic oil supplying paths to the hydraulic pressure coupling elements, and a controller for controlling the electromagnetic proportional valves electronically controls the pressure rise characteristics of the hydraulic pressure coupling elements at the time of speed change, to thereby absorb the speed change shock. On the other hand, because of the manufacturing cost, a control device of non-electronic control type is also employed.
A related control device of the non-electronic control type is designed as follows. That is, an oil supplying path to a predetermined hydraulic pressure coupling element, for instance, a second-speed hydraulic pressure coupling element, of a transmission is provided with an orifice and a bypass path bypassing the orifice, and in the bypass path, a switching (open and close) valve is provided which shuts off the bypass path when the throttle opening degree is small (cf. for instance Japanese Patent Application (OPI) No. 223564/1991 (the term "OPI" as used herein means an "unexamined published application")).
If, when a down-shift operation to the second speed gear by deceleration (i.e, acceleration return) is conducted, the second speed hydraulic pressure coupling element is abruptly coupled, then the second speed gear is established before the speed of the engine is sufficiently increased. And the drive torque on the output side of the transmission is decreased; that is, so-called "acceleration return shock" occurs. However, with the above-described related control device, at the time of the down shift, the bypass path is shut off, so that the hydraulic oil is supplied through the orifice to the second speed hydraulic pressure coupling element. Therefore, the latter is gradually coupled; that is, the acceleration return shock is softened.
If, when the down shift to the second speed gear is conducted by the kick down which occurs when the acceleration pedal is stepped on, the second speed hydraulic pressure coupling element is abruptly coupled, then a problem occurs; that is, the drive torque on the output side of the transmission is abruptly increased; that is, so-called "kick down shock" occurs. The above-described related control device cannot deal with this problem when the throttle opening degree is high; that is, with the related control device, it is impossible to obtain a high operational performance over the whole range of throttle opening degrees.